This invention relates to a pallet changer of the type in which a pallet is moved between a pallet changer body and a table of a machine tool.
Generally, the pallet changer is constructed such that it has an endless track, and several pallets are simultaneously moved along the endless track. A mechanism for switching pallets is provided at a fixed position on the track. This pallet replacing mechanism is used to remove the pallets set on the table of the machine tool to the fixed position, and to carry the pallets from the pallet changer onto the table of the machine tool.
Normally, the endless track is formed into an oval shape or a shape close thereto by a chain or a sprocket. Further, the pallet replacing mechanism has a linear rail track, and the pallets are reciprocatingly moved along the rail track. The reciprocating movement can be carried out by utilizing, for example, a cylinder-piston mechanism or a rack-pinion mechanism. In the pallet replacing system of the type in which the pallets reciprocatingly move in substantially a straight line as described above, it is necessary to keep the destination or the terminal for the pallets vacant without fail.
In the conventional pallet changer, the replacement of pallets is carried out in the following three steps. That is, first, the used pallets set on the table of the machine tool are removed onto vacant places on the pallet changer. Next, the pallets are moved along the endless track to index the pallet to be used next. Finally, a pallet is moved onto the table of the machine tool.
In the pallet replacing operation as described above, attention should be paid to the fact that the destination of the pallets is vacant, as previously mentioned. That is, no pallets should be present at the terminus of the pallet movement. As described above, in the conventional pallet changer, the three operations have to be separately carried out in said order. Accordingly, limits are naturally imposed on the speed of the pallet replacing operation.
Further, in the conventional pallet changer, there exists a problem in that, since main parts of the pallet changer are fixed at the forward portion of the table of the machine tool, it is difficult for an operator to closely approach the table.